1. Field of the Invention
This invention pertains to the field of the removal of water from the surface of various workpieces, particularly, glass workpieces. More particularly, the invention relates to the utilization of solvent drying of workpieces.
2. Description of the Prior Art
A method for the continuous removal of water from a workpiece by means of solvents which do not form an azeotropic mixture that contains large amounts of water or boils considerably below the boiling point of the pure solvent has been disclosed in DOS. No. 17 29 442. In this process, a bath which is in vigorous motion is used which contains, as its main constituent, an organic solvent which is immiscible with water. It has a boiling point of about 20.degree. to 60.degree. C and a density at 20.degree. C of at least about 1.1. The solvent does not form an azeotropic mixture with water which contains more than about 4% by weight water and which boils more than 8.degree. C below the boiling point of the pure solvent.
In addition to a turbulent zone wherein any existing water on the workpiece which is dipped therein is split into droplets, a steady zone is maintained in the bath wherein the existing water forms a water layer.
Anhydrous solvent is introduced into the turbulent zone continuously at a given rate and the water layer is removed continuously from the steady zone.
The water is displaced from the surface of the non-absorbent workpiece by dipping the latter into the turbulent zone of the bath. By subsequent rinsing of the workpieces in the pure organic solvent, the surface active agents which enhance the displacement of the water from the surface of the workpiece, and are added to the dewatering baths for this purpose, are also removed.
It has been found that this method does not yield completely satisfactory results with respect to the drying of optical glasses since spots or dots will remain on the glass surface. The formation of these dots is caused by small traces of water remaining during the drying. These have an adverse effect on the optical properties of the glass and also interfere with the heat treatment of the glass.